(a) Field of the Invention
The present invention relates to a wireless communication system with multiple antennas. More specifically, the present invention relates to an adaptive transmission and receiving method and device in a wireless communication system with multiple antennas.
(b) Description of the Related Art
The MIMO (multiple input multiple output) method, which is a transmission and receiving method using a plurality of antennas at a transmitter and a receiver, is one of the most noteworthy techniques in the wireless/mobile communication systems because of its performance improvement possibilities in increasing spectral efficiencies and diversity of transmission and reception.
One method for increasing data rates from among the transmission and receiving methods with multiple antennas is an SM (spatial multiplexing) method, in which a symbol sequence is divided into a plurality of sequences and transmitted to different transmit antennas. The symbols transmitted through the different antennas according to the SM method can be detected by using an OSIC (ordered successive interference canceller) receiver, a linear receiver based on ZF (zero forcing) or the MMSE (minimum mean square error) criterion, or an optimal ML (maximum likelihood) receiver.
Meanwhile, antenna diversity schemes are widely used to reduce a multi-path fading effect without increasing the data rates. In particular, the transmit diversity method by the Alamouti scheme in the case of two transmit antennas is widely applied to 3rd generation mobile communication systems and broadband radio-access systems, because the transmit diversity method provides simple configurations of the transmitter and the receiver and enables acquisition of diversity of transmit and receive channels. The Alamouti antenna transmit method is an orthogonal STBC (space time block code) for two transmit antennas. However, an orthogonal code exists only when two transmit antennas are provided, and hence, pseudo orthogonal STBCs have been proposed for other numbers of transmit antennas. When such codes are applied in the frequency domain as in the OFDM (orthogonal frequency division multiplexing) transmission, they are called as SFBC (space frequency block code).
As described, since the SM method transmits a different symbol for each transmit antenna, its performance is substantially changed according to features of elements of an MIMO channel, but since the performance of an STBC method is determined not by each element of the MIMO channel but by the summation of the elements, the STBC method is less sensitive to the MIMO channel features, and hence, a desired antenna transmit method can be differentiated according to the channel environments.
A prior art for improving performance such as capacity and quality in the multiple antenna system is disclosed in U.S. Pat. No. 6,351,499 by lospan which varies a number of transmit antennas for SM according to characteristics of the MIMO channel. However, since the number of the transmit antennas is varied, functions of a receiver become complicated, and the prior art does not exploit the advantages of an STBC.
Together with this, an actively applied method for increasing the data throughput in the current state is the adaptive modulation coding method which selects a modulation order and a code rate suitable for desired performance according to an instantaneous state of fading and background noise intensity of a wireless channel, and transmits them variably, thereby increasing the data throughput. The above-noted adaptive modulation coding method is applied to the HSDPA and the 1xEV-DV which are evolved 3rd generation mobile communication systems, and to the wireless LAN system and to the broadband radio access system, and it has been currently developed and commercialized.
However, selection references for channel state information and a modulation and coding method used by the conventional adaptive modulation coding methods are difficult to directly apply to wireless communication systems with multiple antennas that use spatial multiplexing, performance of which is greatly varied according to characteristics of the MIMO channel.